1. Field of the Invention
The present invention relates generally to electromagnetic methods of and an apparatus for stimulating healing of living tissue and more specifically to a method and apparatus for electromagnetic therapy to promote healing of tissue, e.g., electromagnetically stimulating osteogenesis, i.e., bone growth.
2. Discussion of the Prior Art
The process of healing diseased or damaged tissue including bone involves a variety of biochemical, cellular and tissue events, including changes in nuclear material (DNA), protein synthesis, membrane transport, progenitor-mesenchymal cell differentiation and migration, mitosis, etc.
It has long been recognized that properly applied electro-therapy signals can stimulate bone growth in the vicinity of fresh fractures and non-union fractures, and apparently do so by initiating or stimulating the requisite biochemical changes. That is, it has been thought that the stimulation of these cellular growth processes is related to the changing electrical and/or electro chemical environment of the cells present in bone. This electrical change, in turn, causes an alteration in cell behavior resulting in the synthesis of molecules produced by these cells necessary to effect bone healing. The mechanism underlying these events is thought to be an alteration of the interaction of charged species at the cell surface caused by the electrical signal. Because of the uncertainty regarding the most effective modality of electro-therapeutic treatment, including the nature of the electrical signal, and methods for applying the signal to the site of treatment, a substantial amount of research has been undertaken over quite a number of years to determine the most effective parameters.
Extensive research has been conducted in both experimental animal studies and human clinical trials utilizing various specific waveform formats for such treatment, including invasively-coupled, direct-current devices; capacitively-coupled, symmetric and asymmetric waveforms, and electro-magnetically coupled asymmetric waveforms.
There is a substantial body of prior art detailing the materials and methods used to effect electrotherapeutic bone healing, and many of these are described in the Annals of the New York Academy of Sciences, Vol. 238, October 1974, in an article entitled "Electrically Mediated Growth Mechanisms in Living Systems" (Editors, A. R. Liboff and R. A. Rinaldi). Excellent technical reviews of this field are J. A. Spadaro's "Bioelectric Stimulations of Bone Formation: Methods, Models and Mechanisms," in the Journal of Bioelectricity, Volume 1 (1), p. 99, 1982; and the Orthopedic Clinics of North America Symposium on Electrically Induced Osteogenesis, W. B. Saunders Corp. 1984. These reports detail variations in waveform formats for semi-invasive direct current devices, capacitively-coupled symmetric and asymmetric waveforms and inductively-coupled asymmetric waveforms.
All currently used electro-therapy techniques have one or more limitations. For example, invasive or semi-invasive techniques require at least one electrode to be inserted through the patient's skin in the vicinity of the fracture site. As with any surgical technique this will increase the risk of infection and may limit patient mobility and require subsequent operative procedures. The capacitively-coupled systems operate with a low impedance electrical connection but require that the capacitive plates be located adjacent the skin and require that they be gel-coated daily. Obviously this requires consistent patient compliance to be effective and can be annoying to the patient. The electromagnetic inductively-coupled methods and apparatuses require high power consumption waveform generation devices and bulky coil configurations which also limit the mobility of a patient to function normally outside the clinical environment.
The uncertainty regarding the most effective electrotherapeutic parameters that affect treatment is reflected in numerous patents. For instance, U.S. Pat. No. 4,467,808 (Brighton and Pollack) utilizes a 20-100 KHz signal generated by an alternating current power supply for the treatment of osteoporosis in bone. Unidirectional low voltage pulses are provided to the injury site in a non-invasive method described in U.S. Pat. Nos. 4,266,532 (Ryaby) and 4,461,663 (Delgado). A non-invasive capacitively coupled signal is disclosed in U.S. Pat. No. 4,535,775 (Brighton and Pollack). Other patents pertinent to the electro-therapy area are U.S. Pat. Nos. 3,890,953 (Kraus and Viehbach), 3,893,462 (Manning), 3,952,751 (Yanger) and 4,667,809 (Brighton).
Although the above references are primarily directed towards bone growth stimulation, there are also benefits with respect to the electromagnetic stimulation of soft tissues. These benefits are discussed in Black, "Electrical Stimulation of Hard and Soft Tissues in Animal Models," Clinics in Plastic Surgery, 12 (April, 1985) and Frank et al "A Review of Electro-magnetically Enhanced Soft Tissue Healing," IEEE Eng. in Medicine and Biol, (Dec., 1983).
It may be explained here that it generally takes bone fractures, particularly non-union fractures, many weeks or months to heal, and this is true even with the aid of electro-therapy where it has been tried as an adjunct treatment in an experimental setting. Because the presently utilized electro-therapy devices are, with a few exceptions, not truly portable, if the patient is to benefit from electro-therapy, he must have ready access to a source of electric power to effect treatment. Considering the time required for a bone to heal, this constraint is particularly annoying on a day to day basis, and requires that a patient constantly interrupt his daily routine for treatment, which may in turn cause failure of the patient to comply with the required protocol. Also, in most non-union fracture cases it is desirable for the patient to bear weight on the fracture site while maintaining the electromagnetic stimulation. A non-portable device requires the patient to remain limited in movement to the vicinity of the electromagnetic stimulator device.
Therefore, it is apparent that it is desirable to produce a device having the effective features of the devices currently in use but lacking their undesirable features, particularly their power wasting aspects. By creating a more power-efficient electro-therapy device it is possible to considerably reduce the size of the electro-therapy machines, hence permitting the construction of a completely portable device that allows the user to go about his daily routine without being tethered to a source of electric power.
A few inventors have appreciated the practical advantages of having a portable electro-therapy device. It is important to note that portability in the art is taken to mean a device readily carried by the patient without cumbersome support aids, and particularly connotes devices less than two pounds in weight, preferably less than one pound, and no larger than a small pocket camera inasmuch as portable is a relative term. U.S. Pat. No. 4,432,361 (Christensen and Mizoguchi) describes a portable device that has self monitoring features thereby allowing the patient to ascertain its operational status without having to have it checked by a physician, or another person skilled in the use of the device. This invention is an improvement over that described in U.S. Pat. No. 3,842,841 (Brighton and Freidenberg) which does not have the desirable self-monitoring features. Another portable electrotherapy device is described in U.S. Pat. No. 4,574,809 (Talish et al). It shows a device suitable for integration into an orthopedic cast with a signal generator removably mounted in the cast.
It is evident from the foregoing that there is a need for an effective electrotherapeutic method that is not limited by the currently used devices, but rather which employs a truly portable device.